Three United Nations relief workers were beaten to death and burned by Indonesian militias in West Timor yesterday in an attack that overshadowed the opening session of the millennium summit in New York.

Three United Nations relief workers were beaten to death and burned by Indonesian militias in West Timor yesterday in an attack that overshadowed the opening session of the millennium summit in New York.

The killing of the UN staff, as thousands of Indonesians wielding machetes went on a rampage, prompted the evacuation of 54 people to the comparative safety of East Timor and raised the possibility that all foreign staff would be moved out. The eastern part of the island has been under UN administration since an independence referendum last year, while West Timor remains part of Indonesia.

Witnesses said the militiamen, who are opposed to East Timor independence, killed the three foreign UN workers in the office of the UN High Commissioner for Refugees in the town of Atambua and burned their bodies in the street. They were the first civilian UN staff to be killed in Timor.

The UN building was set on fire by the mob, angered by the unsolved death the day before of a militia leader who was accused of committing atrocities in East Timor last year.

In New York, the UN secretary general, Kofi Annan, broke the news of the killings to more than 150 world leaders gathered at the UN headquarters and asked for a minute's silence.

President Bill Clinton departed from his prepared text to say he was "deeply saddened". He urged the Indonesian authorities to put an end to such abuses, as Indonesian President Abdurrahman Wahid stood to join the minute's silence. Mr Wahid said later he feared the attack had been timed to coincide with his visit.

Despite repeated calls from the UN, Indonesia has failed to rein in the militias, who are accused of having links to the Indonesian military. Mr Annan told Mr Wahid at a private meeting last night that the position was "unacceptable", UN spokesman Fred Eckhard said.

UN peacekeepers were on standby last night in Suai, East Timor, to conduct a second evacuation of international and local personnel. UNHCR spokesman Jake Moreland said: "I think a relocation out of West Timor is on the cards."

The UN agencies in West Timor are caring for about 100,000 refugees who fled the violence generated by the independence poll. Atambua is a major refugee centre. The past month has seen an escalation in violence in the camps throughout West Timor.

Yesterday's attack in Atambua is believed by locals to have been a revenge attack sparked by the killing of a prominent militia leader, Olivio Mendoza Moruk, on Tuesday, in the nearby town of Betun.

He was among 19 suspects named earlier this week in connection with the Indonesian investigation into crimes against humanity in East Timor last year.

Moruk's militia was responsible for the massacre of at least 150 people in a church in Suai on 6 September, following the announcement of independence in East Timor.

The UNHCR believes that 80 per cent of those still in West Timor want to return to East Timor, but are deterred by intimidation and misinformation from the militia and by the Indonesian military's inability to provide any real security.

Attempts to disarm and disband the militia by the Indonesian military have failed, prompting the government in Jakarta to declare that their camps will be forcibly closed within six months. There are also fears that anti-independence militia have been infiltrating East Timor.

Two peace-keeping soldiers have died in border skirmishes with armed militia infiltrators in East Timor in recent weeks, and several have been wounded. Although the militia deny any link with the military, human rights organisations operating in West Timor say they have evidence to prove the militia are still being trained, armed and funded by Indonesian special forces.

Before yesterday, the UN had recorded 193 deaths of civilian workers since 1992.